Orthogonal frequency division multiplexing (OFDM) networks and orthogonal frequency division multiple access (OFDMA) networks support the transmission of both broadcast traffic, intended for multiple subscriber stations (i.e., user devices), and unicast traffic, intended for a single subscriber station. A wireless network uses a point-to-multipoint broadcast control channel (BCCH) to transmit specific parameters that enable a subscriber station to identify and access the wireless network. These parameters include system-specific information and cell-specific information.
Some examples of system-specific information are wireless network identification (ID), location area and routing area information, and the like. The cell-specific parameters may include, for example, the current control channel structure and OFDM parameters, such as the cyclic prefix length used in a cell. For example, the broadcast control channel (BCCH) in a UMTS network broadcasts cell-specific and system specific information. The BCCH maps into the BCH transport channel, which maps into the Primary Common Control Physical Channel (P-CCPCH) at the physical layer. There is only one P-CCPCH within a cell site and it carries synchronization and broadcast information for subscriber stations.
The P-CCPCH has a fixed rate of 30 kbps and a spreading factor of 256. The channelization code for the Primary CCPCH is a predefined value known to the subscriber stations. A predefined channelization code (or Walsh code) enables subscriber stations that are not yet connected to the network to decode the BCCH and thereby gain access to the cell-specific and system-specific information.
Unfortunately, conventional wireless systems, including multicarrier networks (e.g., OFDMA networks), use a single broadcast channel to carry the system-specific and cell-specific information. This results in system inefficiency due to broadcast control channel interference between neighboring cells.
Therefore, there is a need for improved OFDM (or OFDMA) transmission systems that minimize broadcast control channel interference between neighboring cells.